fix-1429 maxPoolSize and maxThreadSize should be configurable

[draganpodvezanec-verox]

closes #1429

The seeder thread pool configuration now uses environment variables with fallback to the original default values:

Core pool size: ${GWC_SEEDER_CORE_POOL_SIZE:16}
Uses the GWC_SEEDER_CORE_POOL_SIZE environment variable, defaulting to 16 if not set

Maximum pool size: ${GWC_SEEDER_MAX_POOL_SIZE:32}
Uses the GWC_SEEDER_MAX_POOL_SIZE environment variable, defaulting to 32 if not set

[groldan]

@draganpodvezanec-verox please rebase on top of main now that the build is working back

[aaime]

The changes make sense but the tests are failing:

2025-10-06T08:51:56.3768358Z INFO      org.geowebcache.seed.SeederThreadPoolExecutor - Seeder thread pool executor shut down complete.
2025-10-06T08:51:56.3860502Z 08:51:56,385 [ERROR] Tests run: 5, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.784 s <<< FAILURE! -- in org.geowebcache.seed.SeederThreadPoolExecutorConfigurationTest
2025-10-06T08:51:56.3862502Z 08:51:56,385 [ERROR] org.geowebcache.seed.SeederThreadPoolExecutorConfigurationTest.testInvalidEnvironmentVariableValues -- Time elapsed: 0.529 s <<< ERROR!
2025-10-06T08:51:56.3866218Z org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'gwcSeederThreadPoolExec' defined in class path resource [seeder-thread-pool-test-context.xml]: Unsatisfied dependency expressed through constructor parameter 0: Could not convert argument value of type [java.lang.String] to required type [int]: Failed to convert value of type 'java.lang.String' to required type 'int'; nested exception is java.lang.NumberFormatException: For input string: "invalid"
2025-10-06T08:51:56.3869737Z 	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:756)
2025-10-06T08:51:56.3871439Z 	at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:220)
2025-10-06T08:51:56.3873201Z 	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1372)
2025-10-06T08:51:56.3875366Z 	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1222)
2025-10-06T08:51:56.3877487Z 	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582)
2025-10-06T08:51:56.3879186Z 	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542)
2025-10-06T08:51:56.3881062Z 	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:336)
2025-10-06T08:51:56.3882175Z 	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
2025-10-06T08:51:56.3883254Z 	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:334)
2025-10-06T08:51:56.3884529Z 	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:209)

Did you try to run them locally?